Methods for sample preparation and observation, charged particle apparatus

ABSTRACT

In an SEM observation in a depth direction of a cross section processed by repeated FIB cross-sectioning and SEM observation to correct a deviation in an observation field of view and a deviation in focus, are corrected, the deviations occurring when a processed cross section moves in the depth direction thereof; information on a height and a tilt of a surface of cross section processing area is calculated before the processing, the above information is used, the deviation in a field of view and the deviation in focus in SEM observation, which correspond to an amount of movement of the cross section at a time of the processing, are predicted, and the SEM is controlled based on the predicted values.

CLAIM OF PRIORITY

The present application claims priority from Japanese application JP2005-200833 filed on Jul. 8, 2005, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods of: processing a continuouscross section in a local area of a sample surface of a semiconductordevice, a new material or the like by using a focused ion beam(hereinafter referred to as an FIB); and observing the continuous crosssection by using a scanning electron microscope (hereinafter referred toas an SEM) and the like. The present invention also relates to a chargedparticle beam apparatus used for the methods.

2. Description of the Related Art

In Kato and Otsuka [2003] THE TRC NEWS, No. 84, pp. 40-43, TorayResearch Center, a dual beam apparatus is described in which bothirradiation axes in an FIB system and an electron beam system cross atan acute angle, and in which an image of a single area can be displayedin the form of scanning images of the two beams, that is, an image takenby a scanning ion microscope (hereinafter referred to as an “SIM image”)and an SEM image. As can be expected from the case of the electron beamsystem, by processing and forming a cross section with the FIB (which ishereinafter referred to as “FIB cross-sectioning”), observation of theprocessed cross section using the SEM (the observation with the SEM ishereinafter referred to as “SEM observation”) can be performed withouttilting a sample. By repeatedly performing the FIB cross-sectioning andthe SEM observation, it is possible to accumulate sequentiallycross-sectioned images in a depth direction of a processed surface. Thatis, three dimensional (hereinafter referred to as 3D) observation can beperformed. In Japanese Patent. No. 2852078, a technology is disclosed inwhich heights of a sample surface at a plurality of points are detectedusing a laser beam, and a tilt of the sample surface is calculated byusing the information on heights at the plurality of points.

In the SEM observation in a depth direction of a processed crosssection, by repeatedly performing the FIB cross-sectioning and the SEMobservation, since the processed cross section moves in the depthdirection, a deviation in an observation field of view and a deviationin focus occur in the SEM observation due to the movement of theprocessed cross section.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method by which adeviation in an observation field of view and a deviation in focus inthe SEM observation are corrected, and the SEM observation iscontinuously performed.

As a method by which a field of view and a focus in an SEM observationare caused to track the move of a processed cross section, one mayconsider a method by which a structure, serving as a mark within amoving cross section of a sample, is searched and tracked so that theposition of the field of view is corrected and automatic focusing isachieved by automatically adjusting a focus on a cross section underobservation as needed. However, the correction of the position of thefield of view and the automatic focusing described above requiresearching operations (operations in a control computer) to achieveoptimum states, respectively. Since such searching operations generallyneed several seconds to several tens of seconds to be completed, it isnot possible during this time to perform the SEM observation on theprocessed cross section which is in a correct field of view and infocus.

In the present invention, to solve the above problem, for example, aheight to a surface of a cross section processing area and a slope ofthe surface are calculated in advance, and using the above information,a deviation in a field of view and a deviation in focus in an SEMobservation, which correspond to an amount of movement of a crosssection at a time of processing, are predicted and corrected. A trackingdevice of the present invention is one by which the field of view andthe focus are controlled to come to a predicted state. Since an SEM isto only track a predicted state, FIB cross-sectioning and SEMobservation on a processed cross section can be not only repeatedly butalso simultaneously performed.

In methods of making and observing a sample of the present invention inwhich a cross section formed on a sample surface by processing thesample surface using, for example, an FIB is moved in a direction thecross section moves backward; the cross section is irradiated with anelectron beam from a direction of an axis which obliquely crosses anirradiation axis of the FIB; and the sample cross section moving asabove is observed with the SEM, tilting information on the samplesurface is obtained; using an angle formed by an irradiation axis of theFIB and an irradiation axis of the electron beam and the tiltinginformation on the sample surface, correction coefficients are obtainedwhich correspond to an amount of movement of a field of view of the SEMand an amount of a deviation of a focus position of the same, themovement of a field of view and the deviation of a focus positionoccurring due to moving of the sample cross section at a time ofprocessing the same; and the movement of a field of view and thedeviation of a focus position of the SEM are corrected using thecorrection coefficients, and the field of view and the focus positionare caused to track the moving of the sample cross section.

The tilting information on the sample surface is obtained by using arelationship between a coordinate position of an SIM image of a markformed, for example, on the sample surface and a coordinate position ofthe SEM image of the same. In a rectangular coordinate system with anirradiation axis of the FIB set as a Z_(i) axis and with a planeperpendicular to the Z_(i) axis set as a X_(i)Y_(i) plane, when settingan X_(i) axis within a plane containing the irradiation axis of the FIBand the irradiation axis of the electron beam, the tilting informationon the sample surface corresponds to tilting angles of the samplesurface, the sample surface being tilted relative to the X_(i) axis withrespect to the Y_(i) axis as an axis of rotation. The tilting angle isobtained by using positions of mark images in the SIM image observed fortwo marks having different X_(i) axis directional components, positionsof mark images in an SEM image observed for the two marks, and an angleformed by the irradiation axis of the FIB and the irradiation axis ofthe electron beam.

A charged particle beam apparatus of the present invention in which across section formed on a sample surface by processing the samplesurface using the FIB is moved in a direction the cross section movesbackward; and the sample cross section moving as above is observed withan SEM includes: a sample stage for holding a sample; an FIB system inwhich the FIB is irradiated on the sample held on the sample stage and asample cross section is processed; an electron beam system having anirradiation axis which crosses an irradiation axis of the FIB on thesample; a detector for detecting a sample signal emitted from the sampledue to an irradiation of the FIB or an electron beam; a displayingsection for displaying an SIM image and/or an SEM image; and a beamcontrol section for controlling the FIB system and the electron beamsystem. Further, in the charged particle beam apparatus of the presentinvention, the beam control section holds correction coefficients for anamount of movement of a field of view of the SEM and an amount of adeviation of a focus position of the same, the movement of a field ofview and the deviation of a focus position occurring due to moving ofthe sample cross section at a time of processing the same; corrects themovement of a field of view and the deviation of a focus position of theSEM using the correction coefficients; and controls the field of viewand the focus position to track the moving of the sample cross section.

The beam control section obtains the tilting information on the samplesurface by using a relationship between a coordinate position of an SIMimage of a mark formed on the sample surface and a coordinate positionof a SEM image of the same; and can obtain the correction coefficientsfor the amount of movement of a field of view of the SEM and the amountof a deviation of a focus position of the same by using the angle formedby the irradiation axis of the FIB and the irradiation axis of theelectron beam and the tilting information on the sample surface.

The present invention is capable of causing a field of view and a focusin an SEM observation to track a processed cross section even if theprocessed cross section moves in its depth direction during the repeatedperforming of FIB cross-sectioning and SEM observation of the processedcross section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a charged particle beam apparatusof the present invention.

FIG. 2 is an explanatory view showing examples of a method of making across section sample using an FIB and that of performing an SEMobservation (the case where a sample surface is flat, and consistentwith an X_(i)Y_(i) plane).

FIG. 3 is an explanatory view showing other examples of a method ofmaking a cross section sample using an FIB and that of performing an SEMobservation (the case where a to-be-analyzed surface of a sample isparallel to an X_(i)-axis and is tilted at an angle θ relative to theX_(i)Y_(i) plane).

FIGS. 4A to 4C are explanatory views showing still other examples of amethod of making a cross section sample using an FIB and that ofperforming an SEM observation (the case where although a to-be-analyzedsurface of a sample can be approximated by a plane, it is not parallelto the X_(i) and Y_(i) axes and tilted relative to both axes at anglesθ_(x) and θ_(y), respectively.)

FIG. 5 is a diagrammatic view showing a measuring apparatus, in which alaser microscope is used and a height to a sample surface is denoted asZ.

FIGS. 6A to 6C are explanatory views showing bar-like marks.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described hereinafter withreference to accompanying drawings.

First Embodiment

Referring to FIGS. 1 to 4, an example of a constitution of a chargedparticle beam apparatus is described. FIG. 1 is a schematic blockdiagram of a charged particle beam apparatus of a first embodiment.Hereinafter, as coordinate systems for an FIB system 1, an electron beamsystem 3, and a sample 6, rectangular coordinate systems are adoptedwith coordinates (X, Y, Z) while the coordinates for the irradiationsystem 1, the irradiation system 3, and the sample 6 are differentiatedfrom each other by attaching lower indices i, e, and s, respectively.The FIB system 1 and the electron beam system 3 are attached to a samplechamber 5, and an FIB irradiation axis (−Z_(i)) and an electron beamirradiation axis (−Z_(e)) cross over the sample 6 at an acute angle a(60 degrees in the present embodiment). The angle a at the abovecrossing is a fixed value determined by an apparatus and is known inadvance. At this point of the crossing, coordinate origins O_(i) andO_(e) for the both coordinates are respectively set. For the samplecoordinates, an X_(s)-Y_(s) plane is put over a sample surface, and thecoordinate axis X_(s) is put within a plane spanned by two coordinateaxes Z_(i) and Z_(e). An origin O_(s) is located so that the positionthereof coincides with those of the origins O_(i) and O_(e).

Charged particles and an X-rays emitted from the sample are detected bya charged-particle detector 7 and an X-ray detector 8. Since theposition of the X-ray detector 8 to be provided is hidden behind theelectron beam system 3, the detector 8 is shown under the apparatus inFIG. 1 with that removed from the apparatus. An irradiation systemposition-adjusting section 9 is mechanically moved and adjusted in aplane parallel to an X_(i)Y_(i) plane with the FIB system 1 put over thesample chamber 5, whereby the FIB irradiation axis 2 and the electronbeam irradiation axis 4 approximately cross. In an adjustment carriedout through a mechanical movement, there is a dislocation on the orderof tens of microns left after completely crossing. This dislocation waseliminated by shifting at least one of beam deflection irradiation areasof an irradiation ion beam and an irradiation electron beam. The amountof the above shifting does not come into a transformation betweencoordinates of distance in the following respective coordinates. Thesample 6 is mounted on a sample stage 10 on which the sample 6 iscapable of moving (in the three directions of the X_(i), Y_(i), andZ_(i)-axes of the FIB system), rotating (with respect to the Z_(i)-axisas a rotational axis), and tilting (the Y_(i)-axis being a tiltingaxis). A surface of the sample 6 is adjusted to the crossing point (theorigins O_(i) and O_(e)) of the both irradiation axes as describedabove. A beam control section 15 controls irradiating, scanning, and thelike of a an FIB and an electron beam, and further also controls imagingfor an SEM image, an SIM image, and an X-ray image with chargedparticles, X-rays, and the like, which emit from the sample insynchronization with the scanning and which serve as luminance signals.These images are displayed on an image display device 13 along with awindow image plane for a beam control. In the present embodiment in thedrawing, an SIM image 14 a and an SEM image 14 b are displayed on theimage display device 13. A vacuum pumping system 11 with which thesample chamber is evacuated is driven by a vacuum pumping system power.A SEM observation-field-of-view tracking section 16 to be describedlater is included in the beam control section 15.

FIGS. 2 to 4 are explanatory views for a method of making of a crosssection sample using an FIB and for a method of performing SEMobservation in the present embodiment. FIG. 2 is an aspect of thepresent embodiment in which a local observation surface (X_(s)-Y_(s)plane) of the sample coincides with the X_(i)Y_(i) plane of the ionirradiation system coordinates. A region 21 of the sample on which athree dimensional (3D) analysis is intended to be performed isapproximated by a rectangular parallelepiped having a width W, a depthD, and a length L, with a cross section 20 being an end. Typical sizesof W, D, and L are 8 μm, 8 μm, and 20 μm, respectively.

First, an FIB cross-sectioning is performed on a rectangular opening(width W, depth D, length Lo) 22 so that the cross section 20 isexposed. This cross section is an initial one on which an SEMobservation is performed, and an observation field of view and a focusof an SEM image are adjusted to the above cross section. The crosssection 20 is formed in a rigorous manner so that it is tilted at anangle of 1 to 3 degrees relative to a Y_(i)-Z_(i) plane due tosputtering characteristics of ion. The rectangular opening 22 is used asan incidence path for an electron beam to perform the SEM observation onthe cross section 20. Accordingly, the length Lo of the opening needs tobe at least one on the order of D·tanα.

Next, to perform 3D observation, the processed cross section 20 is movedin a continuous or stepwise manner to −X_(i) direction (in FIG. 2,X_(i,s)→X_(i,2)) by a beam deflection shift in a scanning area of FIBcross-sectioning. When the amount of the movement is large, the field ofview of the SEM observation is displaced to a large extent from theposition X_(i,s) of the cross section, resulting not in focus. A pointof the present invention is that an observation field of view and afocus of an SEM image are caused to track a moving cross section as thecross section moves. To enable the above the tracking, amounts ofcorrection for a deviation in an observation field of view and for adeviation in focus in the SEM observation, the amounts of whichcorrespond to the amount of movement of the processed cross section, aremeasured prior to the operations of cross-sectioning and an observation,and an SEM state may be set as needed according to the above describedamount of correction when performing an operation of cross-sectioning. Amethod of measuring the above amounts of correction is described,hereinafter.

In FIG. 2, when denoting the amount of movement of the cross section 20as ΔX_(i) (>0), values ΔY_(e) and ΔZ_(e) for movement are expressed asfollows in terms of the crossing angle α, which is formed by theelectron beam axis and the FIB axis in the electron beam coordinates.ΔY _(e)=cos α·ΔX _(i)  (1)ΔZ _(e)=−sin α·ΔX _(i)  (2)

That is, as the amounts of correction for the observation field of viewand the focus of the SEM observation, ΔY_(e) and ΔZ_(e) calculated fromthe above respective equations may be set according to the amount of thebeam deflection shift in the scanning area for FIB cross-sectioning.

In FIGS. 2 to 4, and FIG. 6, coordinate axes X_(e)′, Y_(e)′, and Z_(e)′correspond to those obtained by moving the X_(e), Y_(e), and Z_(e) axesin the electron beam system through the translating of the origin O_(e)over the Z_(e)-axis. To avoid overlapping of an explanatory view on theX_(e)Y_(e) plane and another view, a description is given by using theX_(e)′-Y_(e)′ plane which has been translated in parallel over theZ_(e)-axis. The X_(e)Y_(e) plane and the X_(e)′-Y_(e)′ plane arecompletely equivalent. Further, to obtain information on the tiltedangle of a local surface of a to-be-analyzed target portion, symbols b₁to b₄ are provided as marks on a sample surface in the vicinity of thelocal area. These marks are formed on corners of a rectangle havingedges which are parallel to the X_(i) and Y_(i) axes, as remains of FIBcross-sectioning or deposited layers having used FIB-assisteddeposition. Symbols a₁ to a₄ are projections of b₁ to b₄ projected onthe X_(i)Y_(i) plane. Symbols c₁ to c₄ and d₁ to d₄ are projections ofa₁ to a₄ and b₁ to b₄ projected on the X_(e)Y_(e) plane (orX_(e)′-Y_(e)′ plane), respectively. As in Eqs. (1) and (2), when theX_(s)-Y_(s) plane for the sample surface coincides with the X_(i)Y_(i)plane, amounts of correction, ΔY_(e) and ΔZ_(e), can be calculated evenif there are no marks.

Next, referring to FIG. 3, a description is given for the case where alocal surface of a to-be-analyzed target portion of the sample is inparallel to the Y_(i)-axis (i.e. a tilted angle θ_(y)=0 where θ_(y)denotes an angle tilted relative to the Y_(i)-axis) and is, however,tilted at a small angle θ_(x) relative to the X_(i)-axis. Since thetilted angle θ_(x) is an unknown value, it is necessary to find inadvance the value of the tilted angle θ_(x) and seek in advance amountsof correction for a deviation of an observation field of view and for adeviation in focus in order to track the cross section 20 under the SEMobservation. To find out the above tilted angle θ_(x), at least twodifferent kinds of marks having different X_(i) values are provided on asample surface in the vicinity of the position of a sample cross sectionto be made. A local area on the sample to which the marks are providedcan be approximated by a plane. FIG. 3 is an example in which four marksb₁ to b₄ are provided to a sample surface. Since a mark plane(X_(s)-Y_(s) plane) is tilted at an angle θ_(x) relative to theX_(s)-Y_(s) plane, when denoting as β an angle which is formed by themark plane and the Y_(e) axis in the electron beam coordinates, thefollowing relationship between β, θ_(x) and α is established.β=α−θ_(x)  (3)

For the distance between the marks b₁ and b₄ on the sample (hereinafterthe distance between marks is denoted with an underline, e.g., b₁b₄),and for the distances between the marks a₁a₄ and between the marks d₁d₄,in which, using an SIM image and an SEM image, correction is made withimage magnification, and thereafter measurement is made. Thenrelationships among the above distances b₁b₄, a₁a₄ and d₁d₄ arerespectively expressed by using θ_(x) and β as follows.a ₁ a ₄=cos θ_(x) ·b ₁ b ₄  (4)d ₁ d ₄=cos β·b ₁ b ₄  (5)Using Eqs. (3) to (5), the following is obtained.cos(α−θ_(x))/cos θ_(x) =d ₁ d ₄ /a ₁ a ₄  (6)

From the equation above, θ_(x) can be expressed by the followingequation.θ_(x)=arctan[{1−(d ₁ d ₄ /a ₁ a ₄)/cos α)}/tan α]  (7)

Since the distances d₁d₄ and a₁a₄ are measured values obtained by usingthe both images, and α is a known value determined with a charged beamapparatus, the angle θ_(x) can be calculated using Eq. (7). As long asthere are two marks having different X_(i) values such as b₁ and b₄,θ_(x) can be calculated. That is, any other one of the marks b₁ and b₃,b₂ and b₃, and b₂ and b₄ may be accepted. This is because the distancesof projected marks, a₁a₃, a₂a₃, and a₂a₄, the projected marks beingprojections of the above marks projected on the X_(i)Y_(i) plane, havecomponents in the direction of the X_(i)-axis which all coincide withthe distance a₁a₄.

Using a calculated value θ_(x) obtained by Eq. (7), an amount of themovement of a field of view denoted as ΔY_(e) and an amount of thedeviation of a focus position denoted as ΔZ_(e) in the electron beamcoordinates, the both amounts corresponding to the amount of movement ofthe cross section 20 denoted by ΔX_(i), are expressed by Eqs. (8) and(9) being similar to Eqs. (1) and (2), and are predictable in advanceaccording to ΔX_(i) (while ΔX_(e)=0).ΔY _(e) =K _(y) ·ΔX _(i)  (8)ΔZ _(e) =K _(z) ·ΔX _(i)  (9)whereK _(y)=cos(α−θ_(x))/cos θ_(x)  (10)K _(z)=−sin(α−θ_(x))/cos θ_(x)  (11)

Here, K_(y) and K_(z) respectively denote correction coefficients ofΔY_(e) which is the amount of the movement of a field of view and ΔZ_(e)which is the amount of the deviation of a focus position. It is noted,in particular, that if θ_(x) is set as θ_(x)=0 in Eqs. (8) and (9),these equations coincide with Eqs. (1) and (2) Moreover, ΔZ_(i)corresponding to ΔX_(i) is expressed as follows.ΔZ _(i) =ΔX _(i)·tan θ_(x)  (12)

Last, referring to FIG. 4, a description is given for the case wheresmall tilted angle components to the X_(i) and Y_(i) axes on the localsurface of the to-be-analyzed target portion of the sample are θ_(x) andθ_(y), respectively. FIG. 4A is a perspective diagram showing arelationship between the marks b₁ to b₄ formed on the sample surface andthe respective coordinate systems. FIG. 4B is a diagram showingprojected images of the marks b₁ to b₄ projected on the X_(i)Y_(i)plane. FIG. 4C is a diagram showing projected images of marks a₁ to a₄and marks b₁ to b₄, all being projected on the X_(e)Y_(e) plane. As inthe case of FIG. 3, the symbols a₁ to a₄ indicate projected positions(refer to FIG. 4B) of the marks b₁ to b₄ projected on the X_(i)Y_(i)plane; and the symbols c₁ to c₄ and d₁ to d₄ indicate projectedpositions (refer to FIG. 4C) of the symbols a₁ to a₄ and b₁ to b₄projected on the X_(e)Y_(e) plane. Even if the symbols a₁ to a₄ form arectangle, the symbols b₁ to b₄ and d₁ to d₄ form parallelograms becauseof the presence of the tilts θ_(x) and θ_(y). An angle θ_(e,y), which isformed by a tilt of a line segment d₁d₄ in an SEM image to theX_(e)-axis, has a relationship with θ_(y) as expressed by the followingequation.θ_(y)=arctan[tan θ_(e,y)/sin α]  (13)

Setting the positional coordinates of points d_(j) (j=1 to 4) in an SEMimage as (X_(e,j), Y_(e,j)), tanθ_(e,y) can be calculated by thefollowing equation.tan θ_(e,y)=(Y _(e,2) −Y _(e,1))/( X _(e,2) −X _(e,1))  (14)

Here, since the distance ratio, (Y_(e,2)-Y_(e,1))/(X_(e,2)-X_(e,1)),corresponds to a distance ratio, d₂c₂/c₂c₁, in FIG. 4C, θ_(y) can becalculated by Eqs. (13) and (14). An amount of the movement of a fieldof view denoted as ΔY_(e) and an amount of the deviation of a focusposition denoted as ΔZ_(e) in the electron beam coordinates, the bothamounts corresponding to the amount of movement of the cross section 20denoted by ΔX_(i), are expressed by the same equations as Eqs. (8) and(9). θ_(y) is not included in equations for calculating ΔY_(e) andΔZ_(e). There need to be at least three out of the marks b₁ to b₄ inorder to measure a local surface (a plane approximation) tilted in anarbitrary direction, i.e., θ_(y) and θ_(y). However, there needs to be acalculation of only θ_(x) in order to predict ΔY_(e) and ΔZ_(e).Accordingly, it suffices if there are at least two marks havingdifferent X_(i) values, i.e., a pair of marks out of b₁ and b₄, b₁ andb₃, b₂ and b₃, or b₂ and b₃. In a calculation of θ_(x), if the pair isb₁ and b₄, θ_(x) is the same as the one obtained by Eq. (7). For theother pairs (denoted as b_(i), b_(j) in general), if a component of thedistance a_(i)a_(j) in the X_(i)-direction and a component of thedistance d_(i)d_(j) in the Y_(e)-direction are, respectively, expressedas (a_(i)a_(j))_(x) and (d_(i)d_(j))_(y), these components can bemeasured. Accordingly, the following equation, which is equivalent toEq. (7), may be used.θ_(x)=arctan[{1−((d _(i) d _(j))_(y)/(a _(i) a _(j))_(x)/cos α}/tanα]  (15)

Next, a description is given for a procedure of 3D observation in whichFIB cross-sectioning and SEM observation for observing a processed crosssection are repeatedly (or sequentially) performed.

(i) Setting of a 3D Observation Target Area and Positional Adjustment ofa Sample Stage

A size (width W, depth D, length L) and a position of a 3D observationtarget area are determined, and the 3D observation target area isadjusted to the vicinity of an intersection of both of FIB and electronbeams by performing XYZ movement of a sample stage. Next, with ato-be-formed cross section put in parallel to the X_(i)Y_(i) plane, andwith a Y_(i) component of the cross section in a moving direction set tothe value 0, the sample stage is rotated so that an X_(i) component isin the direction of −X_(i) axis.

(ii) Forming of Marks

Four marks are formed in the vicinity of (or to surround) a surface of asetting area in the 3D observation target area. Respective marks areformed at positions corresponding to corners of a rectangle on theX_(i)Y_(i) plane, edges of the rectangle being parallel to the X_(i) andY_(i) axes. Although the number of marks is generally four, which is thesame as the number of corners of a rectangle, it suffices if there areat least three marks out of the four marks. When a local surface of anobservation area is in parallel to the X_(i)Y_(i) plane in particular,marks are not necessary. When the surface is slightly tilted only in adirection of the X_(i) axis, it suffices if there are at least two markshaving different X_(i) values. Although the shape of the mark isnormally a round-shaped opening, or a groove having an “X”-like shape ora “+”-like shape, being cut out by performing FIB cross-sectioning, itmay be a deposited layer locally formed by performing an FIB-assisteddeposition.

(iii) Registration of Positional Coordinates (X_(i), Y_(i)) of FormedMarks

Positional coordinates (X_(i), Y_(i)) of the formed marks areregistered. When the marks are formed by performing FIBcross-sectioning, coordinate data in the cross-sectioning can be used aspositional coordinates (X_(i), Y_(i)) of the marks.

(iv) Observation of an SEM Image of a Mark, and Registration ofPositional Coordinates (X_(e), Y_(e)) thereof

An SEM image of a mark is observed, and positional coordinates (X_(e),Y_(e)) thereof are registered.

(v) Calculation of Tilted Angles θ (θ_(x), θ_(y)) of a To-be-ObservedLocal Sample Surface

Tilted angles θ (θ_(x), θ_(y)) are calculated using Eqs. (7), (13) and(14).

(vi) Calculation of Correction Coefficients K_(y) and K_(z)

Correction coefficients K_(y) and K_(z) for an amount of the movement ofa field of view, ΔY_(e), and an amount of the deviation of a focusposition, ΔZ_(e), are respectively calculated by using Eqs. (10) and(11).

(vii) Setting of Conditions of FIB Cross-Sectioning and a Movement Speedof the Cross Section

FIB conditions (conditions of a beam diameter, a beam current, andirradiation) and a movement speed V_(t) of the cross section areregistered.

(viii) Setting of an Initial Value and a Final Value of X_(i) on theMoving Cross Section

An initial value X_(i,s) and a final value X_(i,e) of X_(i) on themoving cross section are set.

(ix) Forming of a Start Cross Section

In an example of FIG. 2, a left end of the rectangular opening 22 is setin a position a little short of a position represented by the initialvalue X_(i), X_(i,s), for processing the rectangular opening. Then, theside surface of the opening is moved to the position represented by thevalue X_(i,s) by processing the unprocessed portion up to the positionrepresented by the value X_(i,s) under the conditions of the FIBcross-sectioning and irradiation (or scanning). The side surface of theopening thus moved is a start cross section.

(x) Registration of Information of a Field of View and a Focus Positionof an SEM Observation Image of a Start Cross Section

An SEM observation image is adjusted to a start cross section under 3Dobservation, and start values (X_(e,s), Y_(e,s), Z_(e,s)) forinformation on an observation field of view (X_(e), Y_(e)) and that offocus position Z_(e) are registered. Start values (X_(i,s), Y_(i,s)) andfinal values (X_(i,e), Y_(i,e)) for positional information (X_(i),Y_(i)) of a cross section formed by the FIB cross-sectioning are alsoregistered. As the kind of signal for an observation image of an SEMcross section, at least one of secondary electrons, reflected electrons,and X-rays is selected, and registered along with the observationconditions. Then, the observation image of the start cross section isobtained and registered.

(xi) Moving-and-Processing of a Cross Section

A cross section is moved and processed using the FIB for processingwhich is registered in (vii) described above. Concurrently with theprocessing time t, an FIB irradiation area is moved in the −X_(i)direction, and in synchronization therewith, the processed cross sectionis also moved. An amount of the movement (>0) is set as ΔX_(i). ΔX_(i)can be expressed by the product of the movement speed of a cross sectionVs and the processing time t [ΔX_(i)=Vs ·t].

(xii) Calculation of Amount of Correction for Information of anObservation Field of View and a Focus Position in SEM Observation

ΔY_(e) and ΔZ_(e) of amounts of correction (ΔX_(e), ΔY_(e), ΔZ_(e)) forinformation (X_(e), Y_(e), Z_(e)) of an observation field of view and afocus position in an SEM observation are calculated using Eqs. (8) and(9), respectively. For correction coefficients K_(y) and K_(z),calculated values in (vi) are used. ΔX_(e) is constantly set to thevalue 0.

(xiii) Setting of Coordinates of an Observation Field of View and aFocus Position of an SEM Observation Image

Coordinate values (X_(e)+ΔX_(e), Y_(e)+ΔY_(e), Z_(e)+ΔZ_(e)) of anobservation field of view and a focus position of an SEM observationimage are set.

(xiv) Obtaining of SEM Observation Image

An observation image of an SEM cross section is obtained, and recordedas a function of an amount ΔX_(i) of movement of a cross section.Amounts of movement, ΔY_(i) and ΔZ_(i), of the cross section in theY_(i) and Z_(i) directions, which correspond to ΔX_(i), are,respectively, zero and an amount obtained by using Eq. (12) as afunction of ΔX_(i).

(xv) End of Moving-and-Processing

When the processed cross section is moved to the final position(X_(i)=X_(i.e)) set in (viii), the operation of themoving-and-processing is terminated.

(xvi) 3D Analysis of SEM Images

3D images are generated using a sequence of SEM images of cross sectionsrecorded in (xiii) as functions of the amounts of movement (ΔX_(i),ΔY_(i), ΔZ_(i)) or ΔX_(i) of cross sections.

The SEM observation-field-of-view tracking section 16 includes beamcontrol calculation software for achieving the processes (i) to (xv),and a process-observation flow display window. An example of items inthe process-observation flowchart display window of the SEMobservation-field-of-view tracking section 16 is shown in Table 1. Theabove described procedures for respective items are described in thecolumn of Contents. Contents of the beam control calculation softwareare to execute calculations shown in the respective items of theprocedures.

Window Items Contents 1. Positional Adjustment of (i) Setting of a 3DObservation   a Sample Stage Target Area and Positional Adjustment of aSample Stage 2. Marking (ii) Forming of Marks (iii)Registration ofPositional Coordinates (X_(i), Y_(i)) of Formed Marks 3. Observation ofSEM Image iv) Observation of an SEM Image of a Mark, and Registration ofPositional Coordinates (X_(e), Y_(e)) thereof (v) Calculation of TiltedAngles θ (θ_(x), θ_(y)) of a To-be-Observed Local Sample Surface (vi)Calculation of Correction Coefficients K_(y) and K_(z) 4. Registrationof (vii) Setting of Conditions of   Conditions of FIB Cross- FIBCross-Sectioning and a   Sectioning Movement Speed of the Cross-Section(viii) Setting of an Initial Value and a Final Value of X_(i) on theMoving Cross Section 5. Forming of Start Cross (ix) Forming of a StartCross   Section Section 6. Registration of (x) Registration ofInformation of   Conditions of SEM a Field of View and a Focus Position  Observation of an SEM Observation Image of a Start Cross-Section 7.Moving-and-Processing (xi) Moving-and-Processing of a   of CrossSection, and SEM Cross Section   Observation (xii) Calculation of Amountof Correction for Information of an Observation Field of View and aFocus Position in SEM Observation (xiii) Setting of Coordinates of anObservation Field of View and a Focus Position of an SEM ObservationImage (xiv) Obtaining of SEM Observation Image 8. End of Moving-and-(xv) End of Moving-and-Processing   Processing

A kind of luminance signal in an observation process of an SEM image ofthe above moving cross section is described. As the kind of signal, atleast one of a secondary electron, a reflected electron, and an X-ray isselected. When using a secondary electron, since a secondary electrondue to an FIB is mixed with a secondary electron due to an electron beamirradiation of an SEM, temporarily interruption of an FIB irradiation isnecessary while obtaining SEM images. That is, operations of FIBcross-sectioning and SEM observation were repeatedly performed. On theother hand, when using reflected electrons and X-rays for a luminancesignal for SEM images, since there is no signal excitation due to an FIBirradiation, temporarily interruption of an FIB irradiation was notnecessary, and sequential operations of FIB cross-sectioning and SEMobservation were performed.

Referring to FIGS. 6A to 6C, other examples for the shapes of the marksare described. FIG. 6A is a perspective diagram showing relationshipsbetween marks b₁ to b₄ formed on a sample surface and the respectivecoordinate systems; FIG. 6B is a diagram showing projected images of themarks b₁ to b₄ projected on the X_(i)Y_(i) plane; and FIG. 6C is adiagram showing projected images of marks a₁ to a₄ and the marks b₁ tob₄ projected on the X_(e)Y_(e) plane. FIGS. 2, 3, and 4A to 4C arediagrams in the case where marks indicate respective representativepositions, and are isolated. FIG. 6 shows an example in which at leasttwo marks having different X_(i) values are connected, substantiallyforming one mark. For example, two marks, b₂ and b₃, and b₄ and b₁,respectively having different X_(i) values in FIG. 4 are respectivelyconnected, resulting in bar-like marks b₂b₃ and b₄b₁ as shown in FIG. 6.The values X_(i) at both ends of a single bar-like mark correspond toinformation on the X_(i) values of respective marks. Accordingly, a markmay be one representing a single typical point, one bar-like markrepresenting two points, or one which is a combination of one mark andone bar-like mark.

Second Embodiment

Tilting information on a sample surface in a 3D observation target areacan be obtained using a laser microscope. FIG. 5 is a diagrammatic viewshowing a measuring device, in which a laser microscope is used and aheight to a sample surface is denoted as Z. A sample 6 is placed on aXYZ samples stage 31. A surface of the sample 6 is irradiated withillumination light from an illumination lump 40 through a lens 39, ahalf mirror 35, and an objective lens 34. In the meantime, an image ofthe surface of the sample 6 is formed on an image pickup device 36through the objective lens 34. An image signal from the image pickupdevice 36 is mirrored on a monitor device 38 through an image processingdevice 37. The image processing device 37, which is connected to acomputer 43, outputs an image of the sample surface on the monitordevice 38. The Z-axis of the XYZ stage 31 is moved up and down, andthereby an automatic focusing on the surface of the sample 6 isperformed while viewing the monitor device 38. Reference numeral 41denotes a displacement detector which reads an XYZ position of the XYZstage 31, and a value in an XYZ coordinate system, which corresponds toan arbitrary position of the sample 6, is read into a computer 43through an interface circuit 42. The XYZ stage 31 is controlled inresponse to a command from the computer 43 through the interface 42.

A 3D to-be-analyzed sample is placed on the XYZ stage so that X_(i),Y_(i), and Z_(i) axes in a sectional view showing the making of a samplein FIG. 1 are consistent with X, Y, and Z axes on the sample stage.Accordingly, a specific part on the vicinity of a surface to be analyzedis kept being tracked by sequentially focusing the laser microscope onthe specific part, and thereby coordinate values (X_(l), Y_(l), Z_(l))at that point are obtained and registered. Such coordinate positioninformation includes tilting information on a sample surface to beanalyzed. For example, denoting coordinates (X_(l), Y_(l), Z_(l)) of amark b_(j) (j=1 to 4) in FIG. 4A as (X_(lj), Y_(lj), Z_(lj)), θ_(x) andθ_(y) are respectively calculated by the following equations.θ_(x)=arctan[(Z ₁₃ +Z ₁₄ −Z ₁₁ −Z ₁₂)/( X ₁₃ +X ₁₄ −X ₁₁ −X ₁₂)]  (16)θ_(y)=arctan[(Z ₁₃ +Z ₁₄ −Z ₁₁ −Z ₁₂)/( X ₁₃ +X ₁₄ −X ₁₁ −X ₁₂)]  (17)

Accordingly, an amount of movement of a field of view ΔY_(e) and anamount of deviation of a focus position ΔZ_(e) in electron beamcoordinates, which correspond to an amount of movement ΔX_(i) of thecross section 20, can be calculated using Eqs. (8) to (11). The lasermicroscope and the charged particle beam apparatus are connected, andcoordinate position information (or information on θ_(x) and θ_(y)) issent from the laser microscope to a beam control section of the chargedparticle beam apparatus. In this case, the coordinate positioninformation (or information on θ_(x) and θ_(y)), which is obtained bythe laser microscope, is read in through a recording medium, or it needsa key input by an operator, while the laser microscope and the chargedparticle beam apparatus may be in offline. When comparing with themethod employing SIM images and SEM images as described above, themethod using the laser microscope has a drawback that a laser microscopeis necessary other than a charged particle beam apparatus integral withan SEM and an SIM.

1. Methods of preparing and observing a sample in which a cross sectionformed on a sample surface is moved in a direction in which the crosssection moves backward by processing the sample surface using a focusedion beam; in which an electron beam is irradiated on the cross sectionin a direction of an axis obliquely crossing an irradiation axis of thefocused ion beam; and in which the moving sample cross section isobserved with a scanning electron microscope, wherein tiltinginformation on the sample surface is obtained; an angle between anirradiation axis of the focused ion beam and an irradiation axis of theelectron beam as well as the tilting information on the sample surfaceis used, and the correction coefficients are obtained which correspondto an amount of movement of a field of view of the scanning electronmicroscope and an amount of a deviation of a focus position of the same,the movement of a field of view and the deviation of a focus positionoccurring due to the movement of the sample cross section by theprocessing; and the movement of a field of view and the deviation of afocus position of the scanning electron microscope are corrected by useof the correction coefficients, and the field of view and the focusposition are caused to follow the movement of the sample cross section.2. The methods of preparing and observing a sample according to claim 1,wherein the tilt information on the sample surface is obtained by usinga relationship in coordinate position between a scanning ion microscopeimage of a mark formed on the sample surface and a scanning electronmicroscope image of the same.
 3. The methods of preparing and observinga sample according to claim 2, wherein, in a rectangular coordinatesystem with an irradiation axis of the focused ion beam set as a Z_(i)axis, and with a plane perpendicular to the Z_(i) axis set as anX_(i)Y_(i) plane, when setting an X_(i) axis in a plane containing theirradiation axis of the focused ion beam and the irradiation axis of theelectron beam, the tilt information on the sample surface concerns atilting angle of the sample surface from the X_(i)Y_(i) plane and thetilt in the X_(i)Z_(i) plane.
 4. The methods of making and observing asample according to claim 3, wherein the tilting angle is obtained byusing positions of mark images in a scanning ion microscope imageobserved for two marks having different X_(i) coordinate values,positions of mark images in a scanning electron microscope imageobserved for the two marks, and an angle between the irradiation axis ofthe focused ion beam and the irradiation axis of the electron beam. 5.The methods of preparing and observing a sample according to claim 2,wherein the mark is any one of a mark made by the processing by means ofthe scanning focused ion beam and a deposited layer formed by means of abeam-assisted deposition.
 6. The methods of preparing and observing asample according to claim 1, wherein the tilt information on the sampleis obtained by using a laser microscope.
 7. A charged particle beamapparatus in which a cross section formed on a sample surface is movedin a direction in which the cross section moves backward by processingthe sample surface using a focused ion beam; and in which the movingsample cross section is observed with a scanning electron microscope,the charged particle beam apparatus comprising: a sample stage forholding a sample; a focused ion beam system for irradiating a focusedion beam on the sample held on the sample stage, and for thus processinga sample cross section; an electron beam system which has an irradiationaxis crossing an irradiation axis of the focused ion beam on the sample;a detector for detecting a sample signal emitted from the sample due toan irradiation of any one of the focused ion beam and an electron beam;a displaying section for displaying a scanning ion microscope imageand/or a scanning electron microscope image; the images being formed onthe basis of the output from the detector and a beam control section forcontrolling the focused ion beam system and the electron beam system;the charged particle beam apparatus in which the cross section formed ona sample surface is moved in a direction in which the cross sectionmoves back by the processing, wherein the beam control section holdscorrection coefficients for an amount of movement of a field of view ofthe scanning electron microscope and for an amount of a deviation of afocus position of the same, the movement of a field of view and thedeviation of a focus position occurring due to the movement of thesample cross section by the processing; corrects the movement of a fieldof view of the scanning electron microscope and the deviation of a focusposition of the same by using the correction coefficients; and controlsboth the field of view and the focus position of the scanning electronmicroscope so as to follow the movement of the sample cross sectionwhich moves in conjunction with movement of an irradiation position ofthe focused ion beam.
 8. The charged particle beam apparatus accordingto claim 7, wherein the beam control section obtains the tiltinformation on the sample surface by using a relationship in coordinatesposition between a scanning ion microscope image of a mark formed on thesample surface and a coordinate position of a scanning electronmicroscope image of the same; and obtains the correction coefficientsfor the amount of movement of a field of view of the scanning electronmicroscope and for the amount of a deviation of a focus position of thesame, by using the angle between the irradiation axis of the focused ionbeam and the irradiation axis of the electron beam as well as the tiltinformation on the sample surface.
 9. The charged particle beamapparatus according to claim 7, wherein, in a rectangular coordinatesystem with an irradiation axis of the focused ion beam set as a Z_(i)axis and with a plane perpendicular to the Z_(i) axis set as anX_(i)Y_(i) plane, when setting an X_(i) axis in a plane containing theirradiation axis of the focused ion beam and the irradiation axis of theelectron beam, the beam control section determines, as the tiltinformation of the sample surface, the tilt angle on the sample surfacetilting in the X_(i)Z_(i) plane and from the X_(i)Y_(i) plane, by usinga ratio of a difference in X_(i) between two marks having differentX_(i) coordinate values to a difference in Y_(i) values between thecorresponding two marks.